Data transmitted between a baseband unit (BBU) and a remote radio unit (RRU) in a distributed base station includes common information and radio signal information. The common information and the radio signal information may constitute digital fronthaul data in a wireless network according to a standard open interface protocol, and the digital fronthaul data is transmitted in both directions between the BBU and the RRU by using an optical fiber or a cable. The radio signal information may carry one or more pieces of antenna-carrier in-phase/quadrature (I/Q) data.
When the standard open interface protocol is a common public radio interface (CPRI), the digital fronthaul data is referred to as a CPRI frame. In this case, the common information is referred to as a control word (CW), and the radio signal information is referred to as an antenna-carrier (A×C).
In a current system, the CPRI frame is transmitted in a bit transparent transmission manner. Specifically, a transmit end first uses the CPRI frame as a bit stream and encapsulates and maps the CPRI frame to a microwave frame payload to form a microwave air interface frame, then performs IQ modulation and up-conversion on the formed microwave air interface frame to form a microwave radio frequency signal, and finally sends the formed microwave radio frequency signal to a receive end using a microwave air interface. However, as a transmission rate of the CPRI frame increases, microwave signal bandwidth required for transmitting the CPRI frame in the bit transparent transmission manner rapidly increases. Consequently, frequency spectrum utilization is reduced.
A transmit end in an Radio over Radio (ROR)/Analog Radio over Fiber (AROF) system can perform analogue transmission on antenna-carrier I/Q data carried by an A×C in a CPRI frame by directly using a microwave, so as to increase frequency spectrum utilization. However, in the ROR/AROF system, neither the transmit end nor a receive end can learn of an LTE uplink-downlink handover timeslot. Therefore, neither the transmit end nor the receive end in the ROR/AROF system can learn of a transmission timeslot of antenna-carrier I/Q data. In this case, in a transmission timeslot in which an A×C does not carry antenna-carrier I/Q data, power of the A×C sent by the transmit end is extremely low or even zero, so that automatic gain control (AGC) of the receive end automatically amplifies a received CPRI frame. However, in a transmission timeslot in which the A×C includes I/Q data, a gain of the AGC of the receive end sharply decreases because the CPRI frame does not need to be amplified. This causes relatively large jitter of an mean square error (MSE) curve of a microwave link. Consequently, system performance may be reduced.